Choosing between FCP and Avid is like choosing between what kind of car you want to drive. Mercedes or Lexus? Both will get you to work but one might be more expensive and have some features that other does not. With that said that does not mean the other is less attractive because it is more affordable. Avid is double the price of FCP. That is why 50% of the market sales for NLE's are going to FCP according to Apple.
In my experience with both, I've found out that Avid works better for bigger productions such as feature films and TV series. For example, last year's Oscar winner for best movie "Hurt Locker" was edited on Avid. On a feature film you might have multiple editors and Avid is more stream line for bigger productions. With Final Cut Pro it works better with smaller productions such as internet videos. Usually FCP users are the only ones who are editing. Also FCP is more user friendly and the learning curve is shorter.
They both will get the job done. There are few advantages for either systems but ultimately it's still your job as the editor to utilize the system and make a great finished product.
Here at Axiom, we run the full Final Cut Studio system. How about your shop? Avid or Final Cut Pro?